Strategic Structural Modification of Quinoxaline-Based D–A-Type Polymers via Tuning Electron-Withdrawing Substituents for Photovoltaic Applications

Abstract

The development of high-performance polymer donors is crucial to advancing polymer solar cell technology. In this study, a set of quinoxaline (Qx)-based D–A-type polymer donors was systematically developed by introducing various electron-withdrawing substituents to tailor their photovoltaic properties. First, a reference polymer, PDBT–QxF, was rationally designed by linking an electron-donating dithienobenzodithiophene (DTBDT) unit and a monofluorinated Qx via a thiophene linker. Subsequently, chlorinated PDBTCl–QxF was synthesized by introducing additional Cl atoms on the thienyl side groups of the DTBDT donor in PDBT–QxF. Next, the F atoms on the Qx units of PDBT–QxF and PDBTCl–QxF were replaced with the stronger electron-withdrawing cyano (CN) group to yield two cyanated polymers, PDBT–QxCN and PDBTCl–QxCN, respectively. Structural modifications via the introduction of Cl atoms and CN moieties into the DTBDT donor and Qx acceptor positively altered the electronic structures of the polymers and enhanced their charge-carrier mobilities, while suppressing charge recombination. Therefore, attributing to the synergistic effects of the Cl and CN substituents, PDBTCl–QxCN exhibited the highest power conversion efficiency of 15.17% among the studied polymers: PDBT–QxF (9.29%), PDBTCl–QxF (12.09%), and PDBT–QxCN (12.66%).